Cardiovascular responses elicited by stimulation of neurons in the central amygdaloid nucleus in awake but not anesthetized rats resemble conditioned emotional responses.

Cardiovascular responses elicited by electrical stimulation of the central amygdaloid nucleus were examined in awake and anesthetized rats. Stimulation through chronically implanted electrodes evoked increases in arterial pressure and heart rate in awake, freely behaving rats. The responses, which were dependent upon the frequency and the intensity of the stimulus, were not consistently related to the presence of evoked amygdaloid afterdischarges or to evoked behavioral reactions. Following induction of anesthesia, stimuli delivered to the same rats through the same fixed electrodes produced decreases in blood pressure and heart rate. Microinjection of L-glutamate into the amygdala of freely behaving rats also elicited increases in arterial pressure and heart rate, indicating that the cardiovascular changes evoked by electrical stimuli are due to excitation of local neurons rather than fibers of passage. The timing and pattern of the response elicited by electrical stimulation of the amygdala in the awake but not the anesthetized rat closely corresponds with that evoked by an acoustic conditioned emotional stimulus.